Ceramic pigments

ABSTRACT

THE INVENTION RELATES TO CERAMIC PIGMENTS. ZIRCON BASED CERAMIC PIGMENTS MAY BE PREPARED BY CALCINING MIXTURES COMPRISING ZIRCONIUM AND SILICON OXIDE (OR COMPOUNDS CAPABLE OF YIELDING THESE MATERIALS ON CALCINATION) IN THE PRESENCE OF A CHROMOPHORE AND ONE OR MORE MINERALIZER COMPONENTS, THE PROPORTIONS OF ZIRCONIUM OXIDE AND SILICA IN THE MIXTURE BEING SUCH THAT ZIRCONIUM SILICATE IF FORMED ON CALCINATION. IT IS KNOWN, FOR EXAMPLE, THAT BLUE AND YELLOW PIGMENTS MAY BE FORMED BY CALCINING MIXTURES OF THE TYPE DESCRIBED ABOVE IN WHICH THE COLOURING AGENTS ARE, RESPECTIVELY, VANADIUM PENTOXIDE AND PRASEODYMIUM OXIDE AND IN WHICH, IN EACH CASE, MINERALIZER COMPONENTS COMPRISING SOURCES OF ALKALI METAL IONS, FLUORIDE IONS AND EITHER CHLORIDE OR BROMIDE IONS ARE EMPLOYED. WE HAVE NOW DISCOVERED THAT CERAMIC PIGMENTS OF STILL FURTHER ENHANCED COLOUR STRENGTH MAY BE FORMED BY CALCINING MIXTURES OF THE TYPE DESCRIBED ABOVE, IN WHICH THE MINERALIZER COMPONENTS COMPRISE, A SOURCE OF BARIUM IONS, IN ADDITION TO SOURCES OF ALKALI METAL IONS, FLUORIDE IONS AND EITHER CHLORIDE OR BROMIDE IONS.

' June 29, 1971 B. T. BELL CERAMIC PIGMENTS Filed Dec. 22, 1967 FIG. 7.

Plot of Lvs b for glazed files contain/mg 2 2 Sheets-Sheet 1 Vanadium blue glaze stain VZ 727 and VZ 722 (Ugqqgg glaze) b (NBS. Units) June 29,1971 B. 'r. BELL v 3,589,925

' cmumrc rmuEm-s Filed Dec. 22,1967 2 Sheets-Sheet n Spectral Reflectance Cove/(h4g0 Standard) Zircon Vand/um glaze stains VZ 127and 722 fierce/71 ReflectanCe- Q Wavelength Mill/microns Patented June 29, 1971 In particular, we have discovered that a strongly blue- 3,589,925 colouredv ceramic pigment may be prepared by calcining CERAMIC PIGMENT a mixture consisting essentially of zirconium and silicon Bernard Trevor Bell, Tl'ellthflm, stoke-oll-Tlehti England, oxides, one or more compounds capable on calcination assign to Johnson Matthey & Limited London 5 of yielding vanadium pentoxide and compounds which EnglandFiled Dec 22 1967 Se No 693 026 constitute sources of alkali metal ions, barium ions, fluoride ions and chloride ions.

Claims priority, application Great Britain, Dec. 22, 1966,

57 41 Preferably sodium chloride and barium fluoride are Int, Cl, C09 ]/28 used as the sources of alkali metal, barium, fluoride and US. Cl. 106-299 11 Claims chloride ions, and preferably these compounds are present in the calcination mixture in such proportions that they constitute respectively 1%-20% and 0.5 %-10-% by ABSTRACT OF THE DISCLOSURE weight of the mixture.

The invention relates to ceramic pigments Zircon Preferably, the mixture is calcined at a temperature based ceramic pigments may be prepared by calcining 15 Wlthlh the h h to 11500 mixtures comprising zirconium and silicon oxide (or com- Ger Plgmeht h h to the lhvehhoh 15 pounds capable of yielding these materials on calcination) typl cany obtamed by calclmhgf at approxlhl'ately h in the presence of a chromophore and one or more m an Open a Y mlxed corhPoslhoh cohslst' mineralizer components, the proportions of zirconium mg 9 60 Zlrcohhlm oxlde, $11195}, oxide and silica in the mixture being such that zirconium mohlum methvahadatei hahmh huonde and ili t is formed on calcination sodium chlor1de. The crushed ground and Washed product It is known, for example, that blue and yellow pi'g- 1s a strhhg blueheramlc Plgmehtments may be formed by calcining mixtures of the type A Pnor hlgmeht, oh h other hand, m be P described above in which the colouring agents are, repared b chlclmng at approhlmathly lh ah PP spectively, vanadium pentoxide and praseodymium oxide Saggar a mlxthre of 60 zlrcohhlm oxldei slhca, and in which, in each case, mineralizer components comalhmomum lhetavahadate 5 sodhhh hhonde and prising sources of alkali metal ions, fluoride ions and 4 sofhum chlonde; The crushed ground and Washed either chloride or bromide ions are employed. calclnatlon product 1s also a strongly coloured blue We have now discovered that ceramic pigments of Cerahhc h still further enhanced colour strength may be formed by 30 In f h to Inns/[hate the ehhahccd'colohr Strength. of calcining mixtures of the type described above, in which cerahhc P1gmeht s 1h accordahce Wlth the lhvhhhohs the mineralizer components comprise, a source of barium Samp1e of a P art hhle Plgmeht and the P g ions, in addition to sources of alkali metal ions, fluoride accordlng to the invention, both P p as described i d i h hl i or b id i above, were mixed respectively with samples of a white,

zircon opaque glaze maturing at 1070 C., at 2.5%, 5%, 7.5%, and 10% concentrations. The pigmented glaze Th i ti relates to ceramic i w samples were then applied to and fired on white ceramic Zircon based ceramic pigments may be prepared by tilescalcining mixtures comprising zirconium and silicon oxide Reflectance measurements on the glaZed tiles in the (or compounds capable of yielding these materials on 40 red green f blue TegiOIls of the Spectrum calcination) i th presence f a chromophore d one were then obtained wlth a Colormaster differential coloror more mineralizer components, the proportions of imeter- In each case the average of r ta e zirconium oxide and silica in the mixture being such measurements at Tight angles to each other taken as that zirconium silicate is formed on calcination. the base Subsequent Computation of modified Adams A chromophore is a material one or more components Coordinates in an attempt to eliminate directional effects of which imparts colour to the calcined material. For ue to f ce de ectsexample, the chromophores in blue and yellow zircon The reflectance measurements and B g r based ceramic pigments a th oxid f di d with the modified Adams Coordinates L, a and b, derived praseodymium respectively, Compounds which yield such r m them are ta ulated elowoxides on calcination are often employed in the calcination mixture. 3; 1

It 1s known that zirconium slllcate cOlllltalIllIlg at least 10% 10% 5% part of the chromophore 1s formed w en mixtures of 34. 07 mm 31 75 43 90 the above type are calcined. The colour strength of the g: j g 2593 3M3 29,11 34,93 ceramic pigment obtained is dependent on the relative B 54708 62.28 57-67 64-82 L 63.32 67.85 65.78 70.07 amount of chromophore incorporated in the zircon lata tice. This in turn is dependent upon the mineralizer comb ponent or components used in the calcination mixture.

It is known, for example, that strongly coloured blue In both the above and the following tables, reference and yellow pigments may be formed by calcining mix- 121 designates the prior art pigment and reference 122 tures of the type described above in which the colourdesignates the pigment according to the invention. ing agents are, respectively, vanadium pentoxide and praseodymium oxide and in which, in each case, miner- VZr VZr VZr VZr 122 121 122 121 allzer components comprlsmg sources of alkali metal 5% 5% 25% 25% ions, fluoride ions and either chloride or bromide ions 65 m are employed- 2:: R 35.1 401 60 45150 51154 We have now discovered that ceramic pigments of 3. B 62.17 67. 96 69.15 73.41 still further enhanced colour strength may be formed 5 1 55i 39% 13 1 3 by calcining mixtures of the type described above, in b -19.3 -1s.1 --14.8 -12.7 which, the mineralizer components, comprise, a source of barium ions, in addition to sources of alkali metal ions, The Adams coordinate (L) represents the lightness fluoride ions and either chloride or bromide ions. value of the glaze colour on a scale ranging from black to white, the coordinate a represents the redness or greenness of the sample, positive values if a signifying redness and negative values greenness whereas the coordinate [2 represents the blueness or yellowness of the sample. In this case positive values signify yellowness and negative values blueness. The units in each case are N.B.S. units where 0.3 N.B.S. units is the minimum difference in tone or strength detectable by a trained observer.

Inspection of the lightness values shows that in each case the L values of coloured glazes containing the prior art pigment are greater than corresponding L values for those containing the new material, i.e. the pigment prepared according to the invention is stronger than the prior art pigment.

This conclusion is confirmed in FIG. 1 which shows a plot of the lightness values against the blueness values of the coloured glazes containing on the one hand the pigment according to the invention and on the other hand the prior art pigment. It may be seen that the pigments prepared according to the invention and the prior art are of slightly different hue. The difference in hue decreases with increasing pigment concentration, the trials containing of the pigment being nearly a perfect match for 4 halide, the improvement which comprises utilizing as the mineralizer component ((1), alkali metal and barium halides selected from the group consisting of the chlorides, bromides and fluorides, said mineralizer component including a fluoride, and at least one of the other indicated halides.

2. A method according to claim 1 wherein chromophore is vanadium pentoxide tor a compound capable on calcination of yielding vanadium pentoxide.

3. A method according to claim 2 wherein the said compound is sodium metavanadate.

4. A method according to claim 2 wherein the said compound is ammonium metavanadate.

5. A method according to claim 1 wherein the chromophore is praseodymium oxide or a compound capable on calcination o'f yielding praseodymium oxide.

6. A method according to claim 5 wherein the said compound is praseodymium oxylate.

hue. At point X glaze trials containing the new and prior 1.9% of the pigment according to the invention would match, in strength, a glaze containing about 2.8% of the prior art pigment. Thus the new pigment is approximately 50% stronger than the prior art material. Similar results are obtained by comparison of compositions with the same L value.

The colorimeter measurements were confirmed by the spectral reflectance measurement shown in FIG. 2. The drawing is a colour comparison between zircon vanadium blue pigments prepared according to this invention and the prior art. The curves were produced by a UNICAM SP500 spectrophotometer from samples containing 10% of the pigment in the zircon opaque glaze on the white ceramic tiles used in the colorimeter measurements.

The curves are representative of the colour of the two samples recorded in terms of percentage reflectance against wavelength. It should be noted that the reflectance of the sample containing the new pigment is lower at all Wavelenghs than the sample containing the prior art'pigment. That is, the new pigment has a greater tinctorial strength than the prior art pigment.

Another ceramic pigment according to the invention is typically obtained by calcining at 960 C. in a closed saggar, a dry mixed composition consisting of 60 g. zirconium oxide; g silica; 10 g. praseodymium oxylate (Pr (C O IOH O); 5 g. barium fluoride; 10 g. sodium chloride. The crushed ground and washed product is a strong yellow pigment.

What I claim is:

1. In a method of making a zirconium silicate ceramic pigment which comprises calcining a mixture containing (a) a member of the group consisting of zirconium oxide and compounds capable of yielding such oxide on calcination; (b) a member of the group consisting of silicon oxide and compounds capable of yielding such oxide on calcination; components (a) and (b) being present in amounts such that zirconium silicate is formed on calcination; (c) an effective amount of a chromophore selected from the group consisting of vanadium pentoxide, praseodymium oxide and compounds capable of yielding such oxide on calcination; and (d) an effective amount of a mineralizer component comprising an alkali metal 7. A method according to claim 1 wherein the mineralizer component comprises sodium chloride and barium fluoride.

8. A method according to claim 7 wherein sodium chloride and barium fluoride are present in the calcination mixture in such proportions that they constitute respectively 120% and 0.510% by weight of the mixture.

9. A method according to claim 1 wherein the mixture is calcined at a temperature within the range 850- 1150 C.

10. A zirconium silicate ceramic pigment comprising the calcined product of a mixture of (a) zirconium oxide, (b) silicon oxide, components (a) and (b) being present in amounts such that zirconium silicate is formed on calcination, (c) an effective amount of a chromophore selected from the group consisting of vanadium pentoxide and praseodymium oxide and (d) an elfective amount of a mineralizer component comprising alkali metal and barium halides selected from the group consisting of the chlorides, bromides and fluorides, said mineralizer component including a fluoride and at least one of the other indicated halides.

11. A composition for preparing a zirconium silicate pigment by calcining, said composition comprising a mixture containing (a) a member of the group consisting of zirconium oxide and compounds capable of yielding such oxide on calcination; (b) a member of the group consisting of silicon oxide and compounds capable of yielding such oxide on calcination; components (a) and (b) being present in amounts such that zirconium silicate is formed on calcination; (c) an effective amount of a chromophore selected from the group consisting of vanadium pentoxide, praseodymium oxide and compounds capable of yielding such oxide on calcination; and (d) an effective amount of a mineralizer component comprising alkali metal and barium halides selected from the group consisting of the chlorides, bromides and fluorides, said mineralizer component including a fluoride, and at least one of the other indicated halides.

References Cited JAMES E. POER, Primary Examiner 

